1. Field of Invention
This invention relates to medical devices which are implanted in the human body, and particularly, to a medical device used to treat hydrocephalus.
2. Background Discussion
"Hydrocephalus" is the diagnostic term meaning excess water in the brain or cranial vault due to the cerebral spinal fluid flow being blocked. When this occurs, the increased intracranial pressure causes the brain to flatten into a thin shell against the skull. In newborn babies this fluid pressure increase also causes the head to swell which, if left untreated, usually results in death. Hydrocephalus is discussed in greater depth in the "Encyclopedia of Neuroscience" Volume 1, Edited by George Adelman and published by Birkhauser. Medical valve type devices, sometimes referred to as shunts, are used to treat hydrocephalus. In an article entitled "Shunt Obstruction: A preventable Complication?" published in Pediatric Neurosurgery (1993, Volume 19, pages 156-164, C. Sainte-Rose discusses mechanical shunt complications.
As disclosed in U.S. Pat. No. 5,411,473, one type of valve (herein the Glaucoma Valve) has been used to treat glaucoma by allowing aqueous humor to flow from the intraocular chamber of the eye to relieve excess pressure. The Glaucoma Valve uses a membrane under tension to form its own fluid retention chamber. A slit-like opening is along adjoining, overlapping edges of portions of the membrane. The membrane responds to slight changes in fluid pressure and expands or contracts to open or close the opening. When opened, it provides a wide open mouth with parted lips that allows for free flow of fluid through it without any substantial resistance to fluid flow. This feature also substantially reduces the likelihood that the opening will be clogged by particulate matter. In a copending application of the inventor, U.S. Ser. No. 08/592,016, now U.S. Pat. No. 5,728,061, there is disclosed a device for treating individuals with hydrocephalus that uses the Glaucoma Valve. Although this device has several advantages over the prior art, it was not specifically designed for treating infants. The invention disclosed herein is an improvement over this device which is especially designed to be implanted in infants (children typically from about the age of 1 month to 4 years).